Various techniques for applying render to a substrate are known. One of the more common techniques used in housing construction is referred to as “stucco”. This technique makes use of a flat wire reinforcing mesh to facilitate the building up of a solid cladding layer of cementitious plaster over a barking material, which is typically fixed to a light timber or steel frame. The cementitious plaster is usually applied either by hand, or more commonly in recent times by means of shot-crete spraying, in consecutive layers or coats, until the desired cumulative thickness has been achieved. This thickness is typically between 20 and 25 mm. The system has a number of advantages including that it can be formed in a variety of shapes around complex curves, it can be finished in a range of surface textures, and it can provide a solid uniform appearance with adequate impact resistance. However, the conventional stucco render system is also subject to a number of inherent disadvantages.
Firstly, in order to build the sprayed stucco plaster to the required thickness, it must be applied in a multiple of relatively thin layers so as to avoid sagging and wastage. This creates planes of weakness in the render system at the interfaces between the layers, which, if incorrectly applied and treated, can induce cracking, and bonding failures. In the past, this problem has been addressed by the application of a curing agent to the plaster composition. The curing agent is typically sprayed onto the surface of each layer as a film. Because of the water loss at the surface of the plaster, the curing agent must be applied within a relatively short time from when the plaster is sprayed, typically within 15 to 20 minutes. Then, before a further plaster layer can be added, the curing agent must be removed. Otherwise, it can prevent or impede adequate bonding between adjacent layers of the plaster composition. These steps all contribute to the material cost, the time involved, and the expertise required in order to implement the system effectively. The process is also highly specialised, and is susceptible to inconsistent application and operator error.
A further disadvantage is that stucco plaster normally comprises a mix of cement, sand and lime, which is difficult to pump and spray effectively by shot-creting as a wet mix. Accordingly, the operator is usually limited to the use of a day mix formulation. However, the application process then becomes heavily reliant upon the skill of the operator to estimate the appropriate level of water which must be added to the mix “on the fly”, during spraying. This in turn introduces a significant potential for variability in the mix composition, which may influence its shrinkage and crack resistance characteristics, and may thereby adversely affect the durability of the render system.
In an attempt to address this problem, it is known to use modified cement and sand plaster mixes, which are designed to be applied using the more consistent wet mix shot-creting technique. However, such mixtures are difficult to use in high build (i.e. high depth) applications requiring a conventional sand and cement render finish. This is because the presence of modifying polymers in the mix makes it too runny to build to more than about 8 to 10 mm in thickness without the aid of an accelerator. Then, once applied, the accelerated mix becomes too sticky and hard to sponge finish. Consequently, additional decorative texture coatings are required in order to provide the desired sponge finished appearance, which adds further to the time and cost involved in the process overall.
Additional disadvantages include the fact that the conventional stucco system requires highly skilled plasterer in order to achieve a consistent high quality flat finish. Such operators are in limited supply, and are expensive. The system is also prone to shrinkage cracking and surface peeling, particularly when drying in exposed conditions. Furthermore, the system requires lengthy and hence costly waiting times between coats to enable each layer of plaster to hydrate and gain full strength. This requirement is often complicated and protracted by adverse weather conditions and limited site access, thereby further compromising the practical and commercial viability of the system in an increasingly competitive housing market.
It is an object of the present invention to overcome or ameliorate one or more of the disadvantages of the prior art, or at least to provide a useful alternative.